1. Field of the Invention
The present invention relates to communication systems offering both analog signal (e.g., voice) and digital signal (e.g., data) telecommunications services.
2. Description of the Related Art
A majority of telephone service subscribers use analog Plain Old Telephone Services (POTS) when placing ordinary voice telephone calls. POTS is generally delivered over a subscriber loop of copper wires installed between each subscriber and either a local telephone company Central Office or a Digital Loop Carrier (DLC) from which the voice signal is digitally transmitted to a Central Office. The Central Office contains circuit-based switches to interconnect each telephone call, and this circuit-based connection is maintained for the duration of a call.
The increased use of computers in businesses and homes has led to an increased load on such circuit-switched telephone networks. Internet traffic is increasingly being transmitted over telephone networks in the form of data calls. The demand for broadband connections to support speedier Web browsing, faster file transfers, and other high-bandwidth applications is constantly increasing. These kinds of communications generally involve periods of high-rate data transmission with long periods of little or no transmission. For such communications, the short-term, peak bandwidth requirements are very high compared to the long-term, average bandwidth requirements. However, in the prior art, even for short-term peak bandwidth calls, the switch (and other network) resources are dedicated for the entire duration of the call. Although voice conversations can be held simultaneously with data calls over a narrowband connection using specialized software and/or hardware, the quality of the voice call and the bandwidth of the data call are compromised.
With the introduction of Digital Subscriber Line (DSL) services over twisted copper pairs, some of these limitations are removed. Subscribers are offered significantly higher bandwidth, and data calls are routed around the circuit switch, directly to a packet-switched network. In some DSL technologies, such as the Asymmetric Digital Subscriber Line (ADSL) system, an analog voice call can share the pair of copper wires with data traffic by using different frequencies. This capability allows the subscriber to simultaneously make or receive analog voice, fax, or modem calls, while maintaining the full bandwidth of the data connection. Furthermore, in DSL implementations, voice calls can be packetized as part of the packet data stream, and either routed entirely through the packet-switched network (if the other party is on the packet-switched network) or sent to a packet-to-circuit gateway, where packetized voice calls are converted to circuit-based voice calls and passed to the circuit-switched network.
Presently, a service provider offering both voice and data services is constrained by traditional equipment such as DLC components that are designed for circuit-switched voice calls and perhaps packet data, but which cannot offer efficient gateway functionality for packetized voice signals (voice packets). In the prior art, a separate gateway is required to handle these packetized voice signals. This separate (external) gateway converts the packetized voice signals to a digital voice stream before the voice signals are transmitted to a circuit-switched network. Accordingly, there is a need for an improved system and method of communicating multiple voice and data streams over a single subscriber loop, which may provide flexible and efficient use of existing infrastructure and reduce the load on circuit-switched telephone network resources.
A Digital Loop Carrier (DLC) system is a communication system where the information carried over the communication medium is transmitted to a circuit-switched network in a digital format DLC systems are now often used by telephone companies as communication systems for voice, digital data information, and analog data information. Analog signals (e.g. voice or analog data information generated by a modem for transmission over a POTS line) are digitized in the DLC system before transmission to the circuit-switched network. Due to the advent of the Internet, there is an increased need to operate these DLC systems to better serve circuit-based voice signals as well as packetized signals at higher and higher bit rates.
Technologies such as digital subscriber line (DSL) services are being developed to allow both analog (e.g., voice) and digital (e.g., data) signals to be transmitted simultaneously over standard twistedpair copper wire telephone lines at multimegabit rates. DSL is seen as an alternative to the more costly and time-consuming installation of high-speed fiber-based broadband communications networks. Competing DSL technologies include asymmetric DSL (ADSL), high-speed DSL (HDSL), symmetric DSL (SDSL), and very high-speed DSL (VDSL), all of which are referred to generically as xDSL. Each is best suited to a different application, with trade-offs made between signal distance and speed and with each having different transmission bandwidth configurations. ADSL is perhaps the best known DSL variant, providing more transmission bandwidth “downstream” to a telephone subscriber than “upstream” from the subscriber. Downstream transmission rates can be as high as 8 Mbit/s, while upstream transmission rates can be as high as 1 Mbit/s or more, each depending on line quality, distance, and wire gauge. Depending on plant conditions, ADSL can transmit data at a rate of 1.544 Mbit/s over distances of up to 6,000 m (about 18,000 ft) using standard 24-gauge wire, and 8 Mbit/s over distances of 4,000 m (about 12,000 ft) or less. ADSL works by sending digital pulses through the telephone wires using a high-frequency portion of the spectrum. Since these high frequencies are above those used by normal voice communications, ADSL can operate concurrently with voice communication over the same telephone wires.
A Digital Subscriber Line Access Multiplexer (DSLAM) is a piece of electronic equipment that can be used to terminate a DSL loop from a subscriber and multiplex the data from a number of such subscribers onto a network feeder. In the case of ADSL, line or POTS splitters at the carrier divide upstream ADSL transmissions, directing voice communications onto the public switched network and data streams to service providers such as Internet Service Providers (ISPs), and join voice and data streams for downstream transmission. Similarly, a POTS splitter at the subscriber's location similarly joins and splits ADSL transmissions, with voice transmissions terminating at a telephone or other POTS apparatus and data transmissions terminating at an ADSL modem.
A multi-services DLC system is a communication system that can encompass the features of the DLC systems and the DSLAM systems. A multi-services DLC system is capable of handling voice signals, data signals, as well as split voice and data signals. The information carried to the circuit-switched and packet-switched networks from this communications system is in a digital format; however, the signals may be switched in a circuit mode or in a packet mode.
FIG. 1 illustrates an exemplary prior art multi-services digital loop carrier (DLC) system 105. Generally, DLC 105 comprises a DSL line card 109, a packet interface 111, a voice card 113, a controller 115, and a circuit interface 117.
Multi-services DLC 105 may be configured to receive different types of voice signals, e.g., analog voice signals from directly coupled telephones such as telephone 121, analog baseband voice signals from indirectly coupled telephones such as telephone 101, and packetized derived voice signals from indirectly coupled telephones such as telephone 133. Multi-services DLC 105 may also be configured to handle data signals initiated by indirectly coupled computers, such as personal computers 103, and 135, and other data sources.
In particular, telephone 121 is directly coupled to voice card 113. For example, voice card 113 can receive analog voice signals from telephone 121 during a call to telephone 127, convert the analog voice signals to digital voice signals, and forward them to controller 115. Controller 115 receives the digital voice signals from voice card 113 and forwards them to circuit-switched network 125 via circuit interface 117, so that the voice signals may be switched in a conventional circuit-switched manner. Circuit-switched network 125 is a conventional circuit-switched communications network that transports and switches voice traffic, in which a dedicated channel (or circuit) is established for the duration of each call. Circuit-switched network 125 comprises one or more switches interconnected to handle and switch digital signals (e.g., digitized voice signals). This circuit-switched network may be a commonly known public switched telephone network (PSTN), which links together wire segments to create a single unbroken line for each telephone call.
Controller 115 has a plurality of functions including bandwidth management, call processing, and overall control functions. For example, controller 115 may be configured to receive on/off requests from voice card 113 and send ringing requests to voice card 113. The operation and configuration of controller 115 is flexible. For example, controller 115 may be configured in accordance with one or more pre-determined parameters/standards. In another example, controller 115 may be configured to place all incoming calls within one or more specified time slots on circuit interface 117.
Voice card 113 has a dedicated port (equivalent to a phone number) for each directly coupled telephone, e.g., telephone 121. When a directly coupled telephone is not in use, the corresponding port remains idle/unused. Similarly, controller 115 has a one-to-one connection with circuit interface 117, where controller 115 receives voice signals from voice card 113 and forwards them to circuit interface 117, which is configured to communicate with circuit-switched network 125.
Multi-services DLC 105 is also configured to handle composite signals comprising baseband POTS analog voice signals and higher-frequency packetized data signals on a single pair of wires. For exemplary purposes, DLC 105 is shown to receive POTS voice signals and packetized data signals from DSL Customer Premises Equipment (CPE) 107. DSL CPE 107 receives POTS voice signals from telephone 101 and data signals from personal computer 103, and combines and forwards these voice and data signals to digital subscriber loop (DSL) line card 109 of DLC 105.
DSL line card 109 receives the combined baseband POTS voice and data signals from DSL CPE 107, and differentiates between the voice signals and the data signals. The data signals are forwarded to packet interface 111, which further routes the data signals to a packet-switched network 119. Packetswitched network 119 is a packet-switched communications network that transports and switches data packets, in which each message is divided into packets before they are sent. Each packet is then transmitted individually and can even follow different routes to its destination. Once all of the packets forming a massage arrive at the destination, they are recombined to reconstruct the original message. Packet-switched network 119 switches the data signals in a known conventional manner and eventually delivers the data signals to its intended destination, e.g., to a destination personal computer 123.
DSL line card 109 forwards the analog baseband POTS voice signals to voice card 113. Voice card 113 converts the analog voice signals from DSL line card 109 to digital voice signals, and forwards them to controller 115 for forwarding to circuit-switched network 125 via circuit interface 117 for conventional circuit-based switching. Voice card 113 processes analog voice signals received from DSL line card 109 in a similar fashion as if the analog signals had been received from a directly coupled unit, e.g., telephone 121.
Prior art DLCs, such as DLC 105 of FIG. 1, rely on the pre-assignment of ports. In DLC 105, the ports on voice card 113 as well as resources between controller 115 and circuit interface 117 are also preassigned for each directly coupled telephone, e.g., telephone 121, and each indirectly coupled telephone, e.g., telephone 101. Thus, irrespective of the origination points, each type of analog signal is handled by its corresponding ports/resources.
DLC 105 is also capable of handling packetized digital voice signals (i.e., voice packets), typically referred to as derived voice (D-V) signals. The D-V signals are switched and handled in a datalike manner. Generally, D-V signals and associated data signals are communicated via a DSL CPE to the DLC. In FIG. 1, for exemplary purposes, it is shown that DSL CPE 131 receives analog POTS voice signals from originating telephone 133 and packetized digital data signals from personal computer 135. CPE 131 converts the analog POTS voice signals from telephone 133 to D-V signals, and delivers both packetized data and D-V signals to DSL line card 109 of multi-services DLC 105.
DSL line card 109 receives the packetized data and D-V signals from DSL CPE 131 and forwards them to packet interface 111, which routes both packetized data and voice signals to an external packet-switched network, e.g., packet-switched network 119. Packet-switched network 119 comprises the components of a traditional packet-switched network. For example, packet-switched network I19 may comprise one or more packet-based switches configured to switch packetized signals.
The D-V signals are switched in a data-like manner by packet-switched network 119. Packetswitched network 119 differentiates between the derived voice signals and the data signals and, using traditional means, switches the data signals to their intended destination (e.g., personal computer 123). Packet-switched network 119 forwards the D-V signals to a remote packet gateway 129 configured to convert packetized D-V signals to circuit-based digital voice signals, so that the voice signals may be switched in a conventional manner by circuit-switched networks, e.g., circuit-switched network 125. Remote packet gateway 129 is not part of DLC 105. Circuit-switched network 125 switches the circuit-based digital voice signals to its intended destination, e.g., telephone 127.
As described, DLC 105 treats the D-V signals received from CPE 131 differently from analog POTS voice signals (e.g., those received from a directly coupled telephone, such as telephone 121, or those received from an indirectly coupled telephone, such as telephone 101). Unlike POTS signals, D-V signals are handled like data signals and forwarded to packet-switched network 119 via packet interface 111.
Packet-switched network 119 may also receive packetized DV and data signals from remote DSL CPEs coupled via remote DSLAMs (Digital Subscriber Line Access Multiplexers). For exemplary purposes, a remote DSLAM 141 is shown to be coupled to packet-switched network 119. Remote DSLAM 141 may be further coupled to one or more remote DSL CPEs, such as DSL CPE 143. Remote DSL CPE 143 may receive analog POTS voice signals and data packets, respectively, from telephone 145 and personal computer 147, and then packetize the analog voice signals and combine them with the data packets to transmit packetized D-V and data signals to DSLAM 141 using DSL technology. Packets-witched network 119 switches the data signals in a conventional manner, e.g., the data signals may be forwarded to computer 123. In addition, packet-switched network 119 forwards the D-V signals to remote packet gateway 129 for conversion. As described earlier, remote packet gateway 129 converts the D-V signals to circuit-based voice signals, so that these digital signals may be switched by circuit-switched network 125 in a conventional manner.
The multi-services DLC 105 of FIG. 1 is capable of handling different types of voice and data signals. However, this multi-services DLC system is very limited in a few aspects. For example, each origination source, e.g., telephone 101 or telephone 121, has pre-assigned ports/system resources, where system resources refers generally to hardware and software resources on the controller and allocations of bandwidth on internal digital voice links. This requirement of pre-assignment makes it impossible to handle signals from virtual sources. In the case of cell-based voice signals such as those carried over ATM (Asynchronous Transfer Mode), the origination source may vary from call to call or may be unknown. In these instances, prior art DLC 105 is unsuitable, because, in prior art DLC 105, each port on voice card 113 and corresponding resources on controller 115 and circuit interface 117 must be pre-assigned. As such, prior art DLC 105 relies on the use of an external packet gateway, e.g., remote packet gateway 129. This requirement requires additional space and cost.